Natural gas has historically been produced from conventional oil wells or conventional gas wells. In conventional oil wells, the well is drilled into the earth and lined with an outer casing. An inner production tubing is inserted through the outer casing. Oil enters into the production tubing and is raised to the surface through the production tubing. If natural gas is entrained with the oil, it is separated from the oil at the surface and either captured for sale or disposed of. Gas lift or bubble pumps raise fluid such as oil through the incorporation of bubbles of compressed gases such as air, water vapour or other gases thereby reducing the density of the gas/liquid mixture relative to liquid only and carrying liquid oil out of the wellbore. The purpose of gas lift in oil production is to move the oil liquid to the surface for production when the reservoir pressure is insufficient to do so.
In more recent times, coal seam gas has become a significant production source for natural gas. Coal seam gas (CSG) is predominantly methane. CSG collects in underground coal seams by bonding to the surface of coal particles. The coal seams in many coal reservoirs are water saturated and the pressure of the water keeps the gas adsorbed on the surface of the coal.
In order to produce coal seam gas, a well is drilled into a coal seam and an outer casing is used to line the well. The outer casing is arranged so that fluids can enter it from the reservoir, e.g. by having perforations in it in the vicinity of the coal seam. Inner tubing is inserted through the casing. Coal seam gas flows into the outer casing and flows upwardly through the annulus between the outer casing and the inner tubing.
In order for a water saturated well to start producing it is often necessary to initially remove a large portion of the water. This “dewatering” results in a lowering of the reservoir pressure to a point whereby desorption of the methane from the coal surface occurs at a substantial rate. Long periods of dewatering may be required before gas production reaches a maximum rate.
Similar wells are used to produce gas from other non-conventional sources, such as gas from shale and gas from shale oil.
Artificial lift systems such as pumps are used for dewatering. Progressive Cavity Pumps (PCPs) are commonly used for dewatering gas wells due to their ability to pump water which may contain particulate content, such as suspended sand from hydraulic fracturing, coal or soil particles, and dissolved solids. PCP installations typically include a pump motor installed on the wellhead which is connected to a bottom-hole pump by way of a drive rod extending though the production tubing. However, there are significant disadvantages with PCP systems, including, importantly,
High costs associated with pump maintenance or replacement, since the pumps must be withdrawn from the well. Performance issues and maintenance arises from:                Stator failures as a result of fatigue, wear and fluid incompatibility issues etc.        Rotor failures as a result of wear, heat cracking, fatigue issues etc.        Rod string failure as a result of fatigue, excessive torque issues etc. and        Tubing string failures as a result of wear and corrosion issues etc.        
Further operational factors that impact the performance of a PC Pump system are:                Overheating as a result of gas entering the pump causing elastomers to swell and overheat;        Solids which cause plugging;        Incorrect operation of the pump outside of the recommended parameters which are determined by the well characteristics;        Extended periods of inactivity or ‘dry well’ conditions;        Costly work-overs due to failed, malfunctioning or end-of-life PC Pumps; and        PCPs cannot be easily controlled in terms of rotation speed, thereby having a direct impact on variable flow rates.        
It is generally held that gas lift is unsuitable for coal seam gas wells because the intent of the well is to produce gas and not recover liquid as in the case of oil recovery. Introducing additional gas into the well from the surface does not facilitate the transport of gas up the well, or the production of additional gas from the reservoir, and has the significant disadvantage of introducing unwanted diluents such as nitrogen or steam into the produced gas which reduces its value. For these reasons, gas lift is nowhere applied to the recovery of coal seam gas.
As mentioned above, to produce the gas from a coal seam gas formation it is necessary to reduce the pressure in the well so as to induce desorption of the methane from coal and cause it to flow into the well. The reduction in pressure requires the removal of water from the coal seam and that water also flows into the outer casing of the well. Much of this water disengages from the gas under gravity and collects at the bottom of the well and submersible mechanical pumps are typically used to pump the water up through the inner tubing so that it can be removed from the well. It will be understood that if excess water builds up in the bottom of the well, the hydrostatic pressure will tend to suppress the flow of coal seam gas from the coal seam into the well.
Significant solid fines and particulate material are also produced in coal seam gas wells and these tend to flow into the well with the water that flows into the well. This results in a build-up of fines/particulates/solids within the well, which can block the flow of water from the well and also cause significant wear and maintenance issues with the mechanical pumps.
As can be seen, production of coal seam gas requires primary and ongoing dewatering of the wells, which incurs significant costs. Current mechanical lift pumps, which are located at the bottom of the coal seam gas wells, are prone to failure from gas interference and fines production, resulting in high downtime and maintenance costs.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.